Modern heating, ventilation, and air conditioning (HVAC) systems are used in a wide range of environments for various purposes and are relied upon in virtually every industry. These HVAC systems, for example, may be used in single-family homes, multilevel office buildings, or even complex automated computer data centers spanning acres. Modern HVAC systems can provide ventilation, reduce air infiltration, and maintain pressure relationships between spaces in these environments.
At the same time, the costs of operating these systems may be very high. For example, the maintenance and electricity costs for a large HVAC system, such as those used on computer data centers, may cost a company millions of dollars. A typical one-megawatt data center may consume as much as 16 million kilowatt-hours of electricity a year, or the equivalent to the energy consumed by 1400 average U.S. households. The total electric bill for computer servers and data centers has risen to over 100 billion kilowatt-hours of energy annually, costing roughly 7 billion dollars in the US alone. By 2010, world data center electricity use represented between 1.1 and 1.5 percent of world electricity use, while in the U.S., data center electricity use represented between 1.7 and 2.2 percent of the total. At the same time, these servers and data centers contribute to more 0.5 percent of the total U.S. greenhouse gas emissions, which is expected to double by 2020.
These high costs can largely be attributed to these large systems' inefficiencies. Remarkably, while modern HVAC systems may differ in size and power, the systems that are used in high-tech computer data rooms operate largely in the same manner as those used in family homes. Even more extraordinary, the HVAC units that comprise a large HVAC system do not operate together as one would expect of a modern electronic system. These individual units are not controlled by a central controller or computer such that they would work together to maintain the air of the entire environment Instead, each operates independently to maintain the air of its individual space, often competing against each other in managing the temperature, humidity, and pressure in the room. For example, in a modern data room HVAC system, each HVAC unit controls its fans and its cooling valves in response to only its own return airflow temperature sensor readings and does not communicate with the other units or otherwise work with the other units to maintain the temperature of the room.
This manner of operation results in tremendous inefficiency. The limited use of sensors compounded by the lack of direct communications with other HVAC units leads to uneven operations between the units, a situation called “load hopping.” For instance, one unit may be running at full capacity while a neighboring unit runs at low capacity or sits completely idle. Moreover, it leads to constant activations, deactivations and adjustments by each HVAC unit as they each attempt, and often compete, to cool the room to the desired temperature. The units often overshoot the targeted temperature, causing other units to adjust incorrectly in response, resulting in a situation in which there is an infinite loop of readjustments by the units, with the units never hitting their targeted temperature. This causes uneven floor temperature distribution and localized supply air heating. Such a method results in tremendously inefficient power-consumption rate and a greater rate of HVAC unit component failures.
Accordingly, there is an important need for an improved method and system for controlling HVAC to operate more efficiently, particularly by avoiding load hopping and minimizing power consumption. A more efficient method and system for controlling HVAC systems may save corporations, and U.S. households alike, millions of dollars in total power costs each year and reduce greenhouse gas emissions.